Not sure why you want firmware version 1.50 when the current public release firmware version is 2.1.14181 (2018 10 16). If you connect your Prime to your computer via USB cable, and then run the HP Connectivity Kit on your computer, it will download the latest public release firmware automatically (if it doesn't, press Help / Check for update).
Beta versions include this warning from HP:
"Please note that this is a beta version that is still undergoing development and testing before official release. The software and all content found within are provided on an “as is” and “as available” basis. HP Inc. does not give any warranties, whether express or implied, as to the suitability or usability of the software or any of its content. Please report any issues found to email@example.com."
My personal opinion is that beta firmware versions pose no risk to your Prime's hardware. Although they do pose a small risk of clearing your Prime's memory, Prime's contents can be easily backed up using the Connectivity Kit, so it's a trivial task to recover any memory contents that are lost due to installing or using beta firmware. Just perform a backup before upgrading the firmware, and whenever you've programmed something new into your Prime... just like prudence demands during normal use... and then go ahead and use the beta firmware with confidence.
Disclaimer: I don't work for HP. I'm just another happy HP calculator user.